1. Field of the Invention
This invention relates to immunoassaying. Immunoassayings are proving of immense value in medicine and biology for the assaying of the constituents of biological fluids, because of the sensitivity and specificity of such assaying. In immunoassaying procedures, for a given target compound, a synthetic antigen is generally first prepared. Heretofore, this has usually been accomplished by coupling the target compound, or a closely related compound, through a coupling group to a carrier which confers antigenicity to the entire compound. The compound coupled to the carrier is usually known as a hapten and, when coupled, it functions as an antigen determinant by causing the antibodies produced to be specific to it. Thus, the antibodies produced have a distinct and unique character, such that they will bind with only a specific compound or class of compounds. The objective in devising the synthetic antigen-hapten conjugate is to provide a compound which will generate antibodies that are specific to the target compound.
Antibodies are prepared by injecting the synthetic hapten-antigen conjugate into mammals and recovering blood serum from the mammals after they have had time to generate antibodies. Typical mammals are rabbits and goats.
The principal problem is usually synthesizing antigens that are capable of producing antibodies that are sufficiently specific. Biological fluids such as blood and urine frequently contain very closely related compounds and it is common for antibodies to be unable to distinguish the target compound from close relatives, or sometimes even distant ones. The antibody is then considered to be a poor one and is said to have low specificity and high cross-reactivity.
The assay itself is commonly a competitive binding assay. In such an assay, the target compound, which is not necessarily extracted, is allowed to compete with known quantities of a labeled standard to bind with a known quantity of specific antibody. From measurement of the proportion of the labeling in the standard-antibody complex that results, the amount of target compound present can be calculated. Radioactive labeling is particularly convenient. Fluorescence perturbation can be used. Normally it will be necessary to remove any unreacted labeled standard, before making the determination on the antibody complex.
Thyronines include compounds of fundamental importance to the functioning of the thyroid gland namely triiodothyronine (T.sub.3) and thyroxine (T.sub.4) or tetraiodothyronine. Accurate assay of these compounds is essential in understanding, detecting and controlling thyroid disorders. Other compounds of interest in this class are glucagon and thyroid releasing hormone.